Micro Replication.

State-machine replication protocols represent the foundation of many fault-tolerant services. Unfortunately, their inherent complexity makes existing implementations notoriously difficult to debug and test. To address this problem, we propose a novel design approach, micro replication, whose main goal is to reduce bugs and enable replication protocols with improved debuggability properties. At its core, our concept consists of a set of principles that, if followed during protocol design, later significantly facilitate crucial tasks such as bug-source isolation, state-information retrieval, as well as root-cause identification. To achieve this, micro replication organizes a protocol as a composition of specialized modules ("micro replicas") that each encapsulate a particular protocol phase or mechanism, and therefore are easier to test and monitor than traditional monolithic replicas. Besides discussing the underlying ideas of our approach, to show its feasibility we also present and evaluate MIRADOR, the first micro-replicated Byzantine fault-tolerant protocol.